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• Graceful termination of NSApplication with Core Data and Grand Central Dispatch (GCD)

  - by Vincent Mac

  I have an Cocoa Application (Mac OS X SDK 10.7) that is performing some processes via Grand Central Dispatch (GCD). These processes are manipulating some Core Data NSManagedObjects (non-document-based) in a manner that I believe is thread safe (creating a new managedObjectContext for use in this thread). The problem I have is when the user tries to quit the application while the dispatch queue is still running. The NSApplication delegate is being called before actually quitting. - (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender I get an error "Could not merge changes." Which is somewhat expected since there are still operations being performed through the different managedObjectContext. I am then presented with the NSAlert from the template that is generated with a core data application. In the Threading Programming Guide there is a section called "Be Aware of Thread Behaviors at Quit Time" which alludes to using replyToApplicationShouldTerminate: method. I'm having a little trouble implementing this. What I would like is for my application to complete processing the queued items and then terminate without presenting an error message to the user. It would also be helpful to update the view or use a sheet to let the user know that the app is performing some action and will terminate when the action is complete. Where and how would I implement this behavior?

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• Lightweight spinlocks built from GCC atomic operations?

  - by Thomas

  I'd like to minimize synchronization and write lock-free code when possible in a project of mine. When absolutely necessary I'd love to substitute light-weight spinlocks built from atomic operations for pthread and win32 mutex locks. My understanding is that these are system calls underneath and could cause a context switch (which may be unnecessary for very quick critical sections where simply spinning a few times would be preferable). The atomic operations I'm referring to are well documented here: http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/Atomic-Builtins.html Here is an example to illustrate what I'm talking about. Imagine a RB-tree with multiple readers and writers possible. RBTree::exists() is read-only and thread safe, RBTree::insert() would require exclusive access by a single writer (and no readers) to be safe. Some code: class IntSetTest { private: unsigned short lock; RBTree<int>* myset; public: // ... void add_number(int n) { // Aquire once locked==false (atomic) while (__sync_bool_compare_and_swap(&lock, 0, 0xffff) == false); // Perform a thread-unsafe operation on the set myset->insert(n); // Unlock (atomic) __sync_bool_compare_and_swap(&lock, 0xffff, 0); } bool check_number(int n) { // Increment once the lock is below 0xffff u16 savedlock = lock; while (savedlock == 0xffff || __sync_bool_compare_and_swap(&lock, savedlock, savedlock+1) == false) savedlock = lock; // Perform read-only operation bool exists = tree->exists(n); // Decrement savedlock = lock; while (__sync_bool_compare_and_swap(&lock, savedlock, savedlock-1) == false) savedlock = lock; return exists; } }; (lets assume it need not be exception-safe) Is this code indeed thread-safe? Are there any pros/cons to this idea? Any advice? Is the use of spinlocks like this a bad idea if the threads are not truly concurrent? Thanks in advance. ;)

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• Java Concurrency : Synchronized(this) => and this.wait() and this.notify()

  - by jens

  Hello Experts, I would appreciate your help in understand a "Concurrency Example" from: http://forums.sun.com/thread.jspa?threadID=735386 Qute Start: public synchronized void enqueue(T obj) { // do addition to internal list and then... this.notify(); } public synchronized T dequeue() { while (this.size()==0) { this.wait(); } return // something from the queue } Quote End: My Question is: Why is this code valid? = When I synchronize a method like "public synchronized" = then I synchronize on the "Instance of the Object == this". However in the example above: Calling "dequeue" I will get the "lock/monitor" on this Now I am in the dequeue method. As the list is zero, the calling thread will be "waited" From my understanding I have now a deadlock situation, as I will have no chance of ever enquing an object (from an nother thread), as the "dequeue" method is not yet finised and the dequeue "method" holds the lock on this: So I will never ever get the possibility to call "enequeue" as I will not get the "this" lock. Backround: I have exactly the same problem: I have some kind of connection pool (List of Connections) and need to block if all connections are checked. What is the correct way to synchronize the List to block, if size exceeds a limit or is zero? Thank you very much Jens

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• asynchronous pages

  - by lockedscope

  I have just read the multi-threading and custom threading in asp.net articles. http://www.williablog.net/williablog/post/2008/12/16/Custom-Threading-in-ASPNET.aspx http://www.williablog.net/williablog/post/2008/12/16/Multi-Threading-in-ASPNET.aspx I have couple of questions. What does he mean by returning a thread to the pool? Is that thread completely removed from memory or put in to a state that it does not scheduled to CPU(is it in sleep state or whatever)? If that thread is removed from memory how could it survive after async point? How this mechanism works? Are every objects(pages class, request,response etc.) are copied to somewhere else before they are disposed? (Or, is it just waiting in a sleep state and then its waked when async call ends?) He is saying that; "Having said that, making pages asynchronous is not really about improving performance, it is about improving scalability" then he is saying; "I'm sorry to say that it will do nothing for scalability or performance." So which one is true? or for which case(s) are they true?

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• python scritp problem once build and package it

  - by Apache

  hi expert, i've written python script to scan wifi and send data to the server, i set interval value, so it keep on scanning and send the data, it read from config.txt file where i set the interval value to scan, i also add yes/no in my config file, so is 'no' it will scan only once and if 'yes' it will scan according to the interval level, my code as below import time,..... from threading import Event, Thread class RepeatTimer(Thread): def __init__(self, interval, function, iterations=0, args=[], kwargs={}): Thread.__init__(self) self.interval = interval self.function = function self.iterations = iterations self.args = args self.kwargs = kwargs self.finished = Event() def run(self): count = 0 while not self.finished.is_set() and (self.iterations <= 0 or count < self.iterations): self.finished.wait(self.interval) if not self.finished.is_set(): self.function(*self.args, **self.kwargs) count += 1 def cancel(self): self.finished.set() def scanWifi(self): #scanning process and sending data done here obj = JW() if status == "yes": t = RepeatTimer(int(intervalTime),obj.scanWifi) t.start() else: obj.scanWifi() once i package my code, its only run when i set my config file set to 'no' where it scan only once, but when i set my config file to 'yes', there is no progress at all, so i found that there is problem with my class RepeatTimer(Timer) once build, but don't know how to solve can anyone help me thanks

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• CPU friendly infinite loop

  - by Adi

  Writing an infinite loop is simple: while(true){ //add whatever break condition here } But this will trash the CPU performance. This execution thread will take as much as possible from CPU's power. What is the best way to lower the impact on CPU? Adding some Thread.Sleep(n) should do the trick, but setting a high timeout value for Sleep() method may indicate an unresponsive application to the operating system. Let's say I need to perform a task each minute or so in a console app. I need to keep Main() running in an "infinite loop" while a timer will fire the event that will do the job. I would like to keep Main() with the lowest impact on CPU. What methods do you suggest. Sleep() can be ok, but as I already mentioned, this might indicate an unresponsive thread to the operating system. LATER EDIT: I want to explain better what I am looking for: I need a console app not Windows service. Console apps can simulate the Windows services on Windows Mobile 6.x systems with Compact Framework. I need a way to keep the app alive as long as the Windows Mobile device is running. We all know that the console app runs as long as its static Main() function runs, so I need a way to prevent Main() function exit. In special situations (like: updating the app), I need to request the app to stop, so I need to infinitely loop and test for some exit condition. For example, this is why Console.ReadLine() is no use for me. There is no exit condition check. Regarding the above, I still want Main() function as resource friendly as possible. Let asside the fingerprint of the function that checks for the exit condition.

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• Internet Explorer cannot 'fully' load ActiveX Control

  - by K Browne

  Context I am migrating an installer for an ActiveX control from Per-Machine to Per-User. I did this by programming the installer write to HKCU\Software\Classes instead of HKLM\Software\Classes. Problem On my machine (Windows 7 with UAC Enabled), the ActiveX control successfully loads. On the other windows 7 test machines (one with UAC enabled, one with UAC disabled), the control 'partially' loads. What is Partially? When a user visits a page with the ActiveX control, Internet Explorer displays a warning message in a yellow bar on the top of the window. If you click the 'Run add-on' button in the bar, the control becomes visible and begins to run, but Javascript code that tries to access properties of the control return the error: Library not registered. Differences between machines On the dev machine reads from HKCR\CLSID\<GUID> succeed while on the test machines these reads fail. Reads from HKCU succeed on both dev and test machines. Reads from HKLM fail on both test and dev machines. (I collected reads using Sysinternals Process Monitor) Strangely, the keys that Internet Explorer fails to read are clearly visible if I use regedit to view HKCR\CLSID\<GUID> on the test machines. Question What can I do to get the per-user control to load on the test machines? What could cause this difference between the dev machine and the test machines? Why can I see the key in HKCR with RegEdit but Internet Explorer cannot see the key? Any help is appreciated. Thank you.

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• MySQL - How do I inner join sorting the joined data

  - by Gary

  I'm trying to write a report which will join a person, their work, and their hourly wage at the time of work. I cannot seem to figure out the best way to join the person's cost when the date is less than the date of the work. Let's say a person cost $30 per hour at the start of the year then got a $10 raise o Feb 5 and another on Mar 1. 01/01/2010 $30.00 (per hour) 02/05/2010 $40.00 03/01/2010 $45.00 The person put in hours several days which span the rasies. 01/05/2010 10 hours (should be at $30/hr) 01/27/2010 5 hours (again at $30) 02/10/2010 10 hours (at $40/hr) 03/03/2010 5 hours (at $45/hr) I'm trying to write one SQL statement which will pull the hours, the cost per hour, and the hours*cost. The cost is the hourly rate last entered into the system so the cost date is less than the work date, ordered by cost date limit 1. SELECT person.id, person.name, work.hours, person_costs.value, work.hours * person_costs.value AS value FROM person INNER JOIN work ON (person.id = work.person_id) INNER JOIN person_costs ON (person.id = person_costs.person_id AND person_costs.date < work.date) WHERE person.id = 1234 ORDER BY work.date ASC The problem I'm having, the person_costs isn't ordered by date in descending order. It's pulling out "any" value (naturally sorted by record position) which matches the condition. How do I select the first person_cost value which is older than the work date? Thanks!

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• Threads, Sockets, and Designing Low-Latency, High Concurrency Servers

  - by lazyconfabulator

  I've been thinking a lot lately about low-latency, high concurrency servers. Specifically, http servers. http servers (fast ones, anyway) can serve thousands of users simultaneously, with very little latency. So how do they do it? As near as I can tell, they all use events. Cherokee and Lighttpd use libevent. Nginx uses it's own event library performing much the same function of libevent, that is, picking a platform optimal strategy for polling events (like kqueue on *bsd, epoll on linux, /dev/poll on Solaris, etc). They all also seem to employ a strategy of multiprocess or multithread once the connection is made - using worker threads to handle the more cpu intensive tasks while another thread continues to listen and handle connections (via events). This is the extent of my understanding and ability to grok the thousand line sources of these applications. What I really want are finer details about how this all works. In examples of using events I've seen (and written) the events are handling both input and output. To this end, do the workers employ some sort of input/output queue to the event handling thread? Or are these worker threads handling their own input and output? I imagine a fixed amount of worker threads are spawned, and connections are lined up and served on demand, but how does the event thread feed these connections to the workers? I've read about FIFO queues and circular buffers, but I've yet to see any implementations to work from. Are there any? Do any use compare-and-swap instructions to avoid locking or is locking less detrimental to event polling than I think? Or have I misread the design entirely? Ultimately, I'd like to take enough away to improve some of my own event-driven network services. Bonus points to anyone providing solid implementation details (especially for stuff like low-latency queues) in C, as that's the language my network services are written in.

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• Supressing GUI?

  - by Legend

  I am trying to run a plugin designed for Vuze using Java. For this I am using a command like this: /home/x/jre1.6.0_14/bin/java -Dazureus.config.path=/home/x/plugin_directory -Dfile.encoding=ANSI_X3.4-1968 -classpath /home/x/P/lib/swtgraphics2d.jar:/home/x/P/lib/Azureus2.jar:/home/x/P/lib/swt.jar org.gudy.azureus2.ui.swt.Main The problem with this is that the launch is failing with an error: changeLocale: *Default Language* != English (United States). Searching without country.. changeLocale: Searching for language English in *any* country.. changeLocale: no message properties for Locale 'English (United States)' (en_US), using 'English (default)' Invoking main failed java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.aelitis.azureus.launcher.MainExecutor$1.run(MainExecutor.java:37) at java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.swt.SWTError: No more handles [gtk_init_check() failed] at org.eclipse.swt.SWT.error(SWT.java:3910) at org.eclipse.swt.widgets.Display.createDisplay(Display.java:863) at org.eclipse.swt.widgets.Display.create(Display.java:851) at org.eclipse.swt.graphics.Device.<init>(Device.java:152) at org.eclipse.swt.widgets.Display.<init>(Display.java:479) at org.eclipse.swt.widgets.Display.<init>(Display.java:470) at org.gudy.azureus2.ui.swt.mainwindow.SWTThread.<init>(SWTThread.java:84) at org.gudy.azureus2.ui.swt.mainwindow.SWTThread.createInstance(SWTThread.java:59) at org.gudy.azureus2.ui.swt.mainwindow.Initializer.<init>(Initializer.java:110) at org.gudy.azureus2.ui.swt.Main.<init>(Main.java:88) at org.gudy.azureus2.ui.swt.Main.main(Main.java:255) ... 6 more Exception in thread "MainRunner" java.lang.SecurityException: VM exit operation prohibited at org.gudy.azureus2.core3.security.impl.SESecurityManagerImpl$2.checkExit(SESecurityManagerImpl.java:274) at java.lang.Runtime.exit(Unknown Source) at java.lang.System.exit(Unknown Source) at com.aelitis.azureus.launcher.MainExecutor$1.run(MainExecutor.java:42) at java.lang.Thread.run(Unknown Source) I am sure that this is happening because I am running the program on a terminal. Is there a way to supress the GUI or let the program think that the GUI was spawned successfully? Any suggestions?

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• Debugging an unresponsive iPhone UI

  - by buggles

  I have an application that needs to update its display every minute or so. To achieve this I was using performSelector:withObject:afterDelay, calling the selector that most of the time just changes some text in a label based on a very simple (and quick) calculation. [self performSelector:@selector(updateDisplay) withObject:nil afterDelay:60]; Occasionally during an update, I have to go off and get some data from the web, and so I do that in another thread using detachNewThreadSelector. That all worked and the "performSelector after Delay" call completes in a tiny fraction of a second, and only runs once a minute. Despite this, and despite running fine on the simulator, the single button in the app is largely unresponsive, not responding to multiple stabs. So, I had assumed peformSelector:afterDelay would not block, but I'm now wondering if it is blocking in some way? I even tried NOT doing the web-look-up incase this was somehow still impacting the responsiveness. No joy. [NSThread detachNewThreadSelector:@selector(updateFromURL) toTarget:self withObject:nil]; I then pushed it through shark to see if I could see anything obvious. From here I can see the web-lookup is the only thing taking any time, but it is only being done every couple of minutes, and then clearly not running on the main thread. The app itself is consuming a tiny fraction of 1% of the CPU (0.0000034%) over 20 minutes, so it just must be a blocking issue. So, am I missing something about performSelector:afterDelay? What other common newbie mistakes might I be making. If it helps, although I've been developing applications for over 20 years, the previous 10 have been largely Java. Perhaps I have a Java assumption loaded :-) Essentially I have assumed the main thread is like the EDT (only do UI stuff on it, but keep everything else off it).

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• MySQL MyISAM table performance... painfully, painfully slow

  - by Salman A

  I've got a table structure that can be summarized as follows: pagegroup * pagegroupid * name has 3600 rows page * pageid * pagegroupid * data references pagegroup; has 10000 rows; can have anything between 1-700 rows per pagegroup; the data column is of type mediumtext and the column contains 100k - 200kbytes data per row userdata * userdataid * pageid * column1 * column2 * column9 references page; has about 300,000 rows; can have about 1-50 rows per page The above structure is pretty straight forwad, the problem is that that a join from userdata to page group is terribly, terribly slow even though I have indexed all columns that should be indexed. The time needed to run a query for such a join (userdata inner_join page inner_join pagegroup) exceeds 3 minutes. This is terribly slow considering the fact that I am not selecting the data column at all. Example of the query that takes too long: SELECT userdata.column1, pagegroup.name FROM userdata INNER JOIN page USING( pageid ) INNER JOIN pagegroup USING( pagegroupid ) Please help by explaining why does it take so long and what can i do to make it faster. Edit #1 Explain returns following gibberish: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE userdata ALL pageid 372420 1 SIMPLE page eq_ref PRIMARY,pagegroupid PRIMARY 4 topsecret.userdata.pageid 1 1 SIMPLE pagegroup eq_ref PRIMARY PRIMARY 4 topsecret.page.pagegroupid 1 Edit #2 SELECT u.field2, p.pageid FROM userdata u INNER JOIN page p ON u.pageid = p.pageid; /* 0.07 sec execution, 6.05 sec fecth */ id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE u ALL pageid 372420 1 SIMPLE p eq_ref PRIMARY PRIMARY 4 topsecret.u.pageid 1 Using index SELECT p.pageid, g.pagegroupid FROM page p INNER JOIN pagegroup g ON p.pagegroupid = g.pagegroupid; /* 9.37 sec execution, 60.0 sec fetch */ id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE g index PRIMARY PRIMARY 4 3646 Using index 1 SIMPLE p ref pagegroupid pagegroupid 5 topsecret.g.pagegroupid 3 Using where Moral of the story Keep medium/long text columns in a separate table if you run into performance problems such as this one.

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• Log4Net GetLogger creates rolling files even for the unreferenced files

  - by ybastiand

  Hi, I have a C# solution that contains three executables. I have each of these three executables sharing the same log4net configuration file. At startup of each of the executable, they retrieve a logger (one logger per executable, as per configuration file further below). When one of the executable performs Log.GetLogger(), it creates all the rolling files instead of only the one rolling file that is referred to as appender-ref in the executable's logger configuration. For instance, when I startup my sending daemon executable, it performs Log.GetLogger("SendingDaemonLogger") which creates 3 files Log/RuleScheduler.txt, Log/NotificationGenerator.txt and Log/NotificationSender.txt instead of only the desired Log/NotificationSender.txt. Then when I startup another of the executables, for instance the rule scheduler daemon, this other process cannot write in Log/RuleScheduler.txt because it has been created and locked by the sending daemon process. I am guessing that there may be three different solutions to my problem: The GetLogger should only create the rolling file appenders that are referenced in the config I should have one config file per executable, this way each config file could list only one rolling file appender and starting each of the executable would not create the rolling files of the other daemons. I am however reluctant to do this because some of the configuration (SMTP appender, console appender) is shared between the daemons and I don't want to have duplicate copies to maintain. Unless there is a way to have a config file including another one? Maybe there is a way to configure the rolling file so that concurrent access across processes is allowed? This solution still isn't perfect in my opinion because any of the daemons should not be creating the rolling files of some other daemons. Thanks in advance for your help! I have difficulties for posting the config file properly here (this website interprets as HTML). Please go to the following link for seeing my log4net configuration file: log4Net configuration file

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• How to improve performance of non-scalar aggregations on denormalized tables

  - by The Lazy DBA

  Suppose we have a denormalized table with about 80 columns, and grows at the rate of ~10 million rows (about 5GB) per month. We currently have 3 1/2 years of data (~400M rows, ~200GB). We create a clustered index to best suit retrieving data from the table on the following columns that serve as our primary key... [FileDate] ASC, [Region] ASC, [KeyValue1] ASC, [KeyValue2] ASC ... because when we query the table, we always have the entire primary key. So these queries always result in clustered index seeks and are therefore very fast, and fragmentation is kept to a minimum. However, we do have a situation where we want to get the most recent FileDate for every Region, typically for reports, i.e. SELECT [Region] , MAX([FileDate]) AS [FileDate] FROM HugeTable GROUP BY [Region] The "best" solution I can come up to this is to create a non-clustered index on Region. Although it means an additional insert on the table during loads, the hit isn't minimal (we load 4 times per day, so fewer than 100,000 additional index inserts per load). Since the table is also partitioned by FileDate, results to our query come back quickly enough (200ms or so), and that result set is cached until the next load. However I'm guessing that someone with more data warehousing experience might have a solution that's more optimal, as this, for some reason, doesn't "feel right".

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• Microsoft Detours - DetourUpdateThread?

  - by pault543

  Hi, I have a few quick questions about the Microsoft Detours Library. I have used it before (successfully), but I just had a thought about this function: LONG DetourUpdateThread(HANDLE hThread); I read elsewhere that this function will actually suspend the thread until the transaction completes. This seems odd since most sample code calls: DetourUpdateThread(GetCurrentThread()); Anyway, apparently this function "enlists" threads so that, when the transaction commits (and the detours are made), their instruction pointers are modified if they lie "within the rewritten code in either the target function or the trampoline function." My questions are: When the transaction commits, is the current thread's instruction pointer going to be within the DetourTransactionCommit function? If so, why should we bother enlisting it to be updated? Also, if the enlisted threads are suspended, how can the current thread continue executing (given that most sample code calls DetourUpdateThread(GetCurrentThread());)? Finally, could you suspend all threads for the current process, avoiding race conditions (considering that threads could be getting created and destroyed at any time)? Perhaps this is done when the transaction begins? This would allow us to enumerate threads more safely (as it seems less likely that new threads could be created), although what about CreateRemoteThread()? Thanks, Paul For reference, here is an extract from the simple sample: // DllMain function attaches and detaches the TimedSleep detour to the // Sleep target function. The Sleep target function is referred to // through the TrueSleep target pointer. BOOL WINAPI DllMain(HINSTANCE hinst, DWORD dwReason, LPVOID reserved) { if (dwReason == DLL_PROCESS_ATTACH) { DetourTransactionBegin(); DetourUpdateThread(GetCurrentThread()); DetourAttach(&(PVOID&)TrueSleep, TimedSleep); DetourTransactionCommit(); } else if (dwReason == DLL_PROCESS_DETACH) { DetourTransactionBegin(); DetourUpdateThread(GetCurrentThread()); DetourDetach(&(PVOID&)TrueSleep, TimedSleep); DetourTransactionCommit(); } return TRUE; }

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• Pthread Queue System

  - by Wallace

  Hi. I'm working on my assignment on pthreads. I'm new and never touched on pthreads before. Is there any sample codes or resources out there that anyone of you have, that might aid me in my assignment? Here are my assignment details. A pthread program about queue system: Write a C/C++ Pthread program for a Dental clinic’s queuing system that declares an array of integers of size N, where N is the maximum number of queue for the day. The pthread program uses two threads. Whenever there is a new dental appointment, the first thread (the creator) puts the queue numbers in the array, one after the other. The second thread (the remover) removes the queue numbers from the array whenever the dentist has seen the patient. This is done in a FIFO fashion (First In First Out). The algorithm of the creator is as follows: • If the array is not full then put a new number in it (the numbers start at 1 and are incremented by one each time, so the creator create queue number 1, 2, 3 etc.) • sleep for 1 to 10 seconds, randomly • repeat The algorithm of the remover is as follows: • If the array is not empty then remove its smallest queue number • sleep for 1 to 10 seconds, randomly • repeat You should use mutex locks to protect things that must be protected. Each thread should print on the screen what it is doing (eg: "number 13 is added into the queue", "number 7 is removed from the queue", etc.). The program should run forever. Any help will be appreciated. Thanks.

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• Performance issue on Android's MapView Navigation-App

  - by poeschlorn

  Hey Guys, I've got a question on making an navigation app more faster and more stable. The basic layer of my app is a simple mapview, covered with several overlays (2 markers for start and destination and one for the route). My idea is to implement a thread to display the route, so that the app won't hang up during the calculation of a more complex route (like it does right now). After implementing the thread there are no updates shows any more, maybe you can help me with a short glance at an excerpt of my code below: private class MyLocationListener implements LocationListener { @Override public void onLocationChanged(Location loc) { posUser = new GeoPoint((int) (loc.getLatitude() * 1E6), (int) (loc .getLongitude() * 1E6)); new Thread(){ public void run(){ mapView.invalidate(); // Erase old overlays mapView.getOverlays().clear(); // Draw updated overlay elements and adjust basic map settings updateText(); if(firstRefresh){ adjustMap(); firstRefresh = false; } getAndPaintRoute(); drawMarkers(); } }; } Some features have been summarized to a method like "drawMarkers()" or "updateText()"...(they don't need any more attention ;-))

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• A error about "Address 0x0 is not stack'd, malloc'd or (recently) free'd" in c program under linux

  - by MaiTiano

  There is a piece of my program: height = atoi(argv[3]); width = atoi(argv[2]); sprintf(seqName,"%s", argv[1]); // strcpy(seqName, argv[1]); After compiling it, a exe file test is generated, then I use Valgrind to check it. Then I got the following message, however I cannot understand what it tends to tell me. Can anyone provide some kind help, Thanks. 1 contexts (suppressed: 13 from 8) 1 contexts (suppressed: 13 from 8) jl@ubuntu:~/work/dsr_analysis$ valgrind --tool=memcheck --leak-check=yes ./test ==28940== Memcheck, a memory error detector ==28940== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al. ==28940== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info ==28940== Command: ./test ==28940== ==28940== Invalid read of size 1 ==28940== at 0x40260CA: strcpy (mc_replace_strmem.c:311) ==28940== by 0x804A5C6: main (me_search.c:1428) ==28940== Address 0x0 is not stack'd, malloc'd or (recently) free'd ==28940== ==28940== ==28940== Process terminating with default action of signal 11 (SIGSEGV) ==28940== Access not within mapped region at address 0x0 ==28940== at 0x40260CA: strcpy (mc_replace_strmem.c:311) ==28940== by 0x804A5C6: main (me_search.c:1428) ==28940== If you believe this happened as a result of a stack ==28940== overflow in your program's main thread (unlikely but ==28940== possible), you can try to increase the size of the ==28940== main thread stack using the --main-stacksize= flag. ==28940== The main thread stack size used in this run was 8388608. ==28940== ==28940== HEAP SUMMARY: ==28940== in use at exit: 0 bytes in 0 blocks ==28940== total heap usage: 0 allocs, 0 frees, 0 bytes allocated ==28940== ==28940== All heap blocks were freed -- no leaks are possible ==28940== ==28940== For counts of detected and suppressed errors, rerun with: -v ==28940== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 13 from 8)1 contexts (suppressed: 13 from 8) 1 contexts (suppressed: 13 from 8)

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• Putting a C++ Vector as a Member in a Class that Uses a Memory Pool

  - by Deep-B

  Hey, I've been writing a multi-threaded DLL for database access using ADO/ODBC for use with a legacy application. I need to keep multiple database connections for each thread, so I've put the ADO objects for each connection in an object and thinking of keeping an array of them inside a custom threadInfo object. Obviously a vector would serve better here - I need to delete/rearrange objects on the go and a vector would simplify that. Problem is, I'm allocating a heap for each thread to avoid heap contention and stuff and allocating all my memory from there. So my question is: how do I make the vector allocate from the thread-specific heap? (Or would it know internally to allocate memory from the same heap as its wrapper class - sounds unlikely, but I'm not a C++ guy) I've googled a bit and it looks like I might need to write an allocator or something - which looks like so much of work I don't want. Is there any other way? I've heard vector uses placement-new for all its stuff inside, so can overloading operator new be worked into it? My scant knowledge of the insides of C++ doesn't help, seeing as I'm mainly a C programmer (even that - relatively). It's very possible I'm missing something elementary somewhere. If nothing easier comes up - I might just go and do the array thing, but hopefully it won't come to that. I'm using MS-VC++ 6.0 (hey, it's rude to laugh! :-P ). Any/all help will be much appreciated.

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• How can I speed up Subversion checkins? (Using ANKH, latest, Visual Studio 2010)

  - by Timothy Khouri

  I've started working on a new web project with some friends... we are using the latest Subversion server (installed last week), the latest version of ANKH. My web project is a whapping 1.5 megabytes (that's with all images, css files, dll's after compiling, pdb files... etc). Checking in even super small changes (literally adding the letter "x" to a few files for testing)... takes FOREVER! (about 10 seconds - I almost killed myself). The ANKH client is measuring in BYTES PER SECOND ... BYTES? per second... I must be doing something wrong. Does anyone what config file has a joke totallyMessWithPeople=true so that I can turn that off or something? Oh, also, changing one "big" file of a super 10k gains speed up to nearly the speed of light (which is apparently 857 bytes per second). Help me obi wan kenobi, your my only hope! EDIT: As a note... my real work project that uses Visual Source Safe 2005 (I know, ouch) uploads files at about 200-500kbps from this very same computer/internet connection.

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• Total Order between !different! volatile variables?

  - by andreas

  Hi all, Consider the following Java code: volatile boolean v1 = false; volatile boolean v2 = false; //Thread A v1 = true; if (v2) System.out.println("v2 was true"); //Thread B v2 = true; if (v1) System.out.println("v1 was true"); If there was a globally visible total order for volatile accesses then at least one println would always be reached. Is that actually guaranteed by the Java Standard? Or is an execution like this possible: A: v1 = true; B: v2 = true; A: read v2 = false; B: read v1 = false; A: v2 = true becomes visible (after the if) B: v1 = true becomes visible (after the if) I could only find statements about accesses to the same volatile variable in the Standard (but I might be missing something). "A write to a volatile variable (§8.3.1.4) v synchronizes-with all subsequent reads of v by any thread (where subsequent is defined according to the synchronization order)." http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.4.4 Thanks!

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• Creating a QMainWindow from Java using JNI

  - by ebasconp

  Hi everybody: I'm trying to create a Qt main windows from Java using JNI directly and I got a threading error. My code looks like this: Test class: public class Test { public static void main(String... args) { System.out.println(System.getProperty("java.library.path")); TestWindow f = new TestWindow(); f.show(); } } TestWindow class: public class TestWindow { static { System.loadLibrary("mylib"); } public native void show(); } C++ impl: void JNICALL Java_testpackage_TestWindow_show (JNIEnv *, jobject) { int c = 0; char** a = NULL; QApplication* app = new QApplication(c, a); QMainWindow* mw = new QMainWindow(); mw->setWindowTitle("Hello"); mw->setGeometry(150, 150, 400, 300); mw->show(); QApplication::exec(); } and I get my window painted but frozen (it does not receive any event) and the following error message when instantiating the QMainWindow object: QCoreApplication::sendPostedEvents: Cannot send posted events for objects in another thread I know all the UI operations must done in the UI thread but in my example I created the QApplication in the only thread I have running, so, everything should work properly. I did some tests executing the code of my "show" method from a QMetaObject::invokeMethod stuff using Qt::QueuedConnection but nothing works properly. I know I could use Jambi... but I know that it could be done natively too and that is what I want to do :) Any ideas on this? Thanks in advance! Ernesto

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• multithreading issue

  - by vbNewbie

  I have written a multithreaded crawler and the process is simply creating threads and having them access a list of urls to crawl. They then access the urls and parse the html content. All this seems to work fine. Now when I need to write to tables in a database is when I experience issues. I have 2 declared arraylists that will contain the content each thread parse. The first arraylist is simply the rss feed links and the other arraylist contains the different posts. I then use a for each loop to iterate one while sequentially incrementing the other and writing to the database. My problem is that each time a new thread accesses one of the lists the content is changed and this affects the iteration. I tried using nested loops but it did not work before and this works fine using a single thread.I hope this makes sense. Here is my code: SyncLock dlock For Each l As String In links finallinks.Add(l) Next End SyncLock SyncLock dlock For Each p As String In posts finalposts.Add(p) Next End SyncLock ... Dim i As Integer = 0 SyncLock dlock For Each rsslink As String In finallinks postlink = finalposts.Item(i) i = i + 1 finallinks and finalposts are the two arraylists. I did not include the rest of the code which shows the threads working but this is the essential part where my error occurs which is basically here postlink = finalposts.Item(i) i = i + 1 ERROR: index was out of range. Must be non-negative and less than the size of the collection Is there an alternative?

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• How to properly close a UDT server in Netty 4

  - by Steffen

  I'm trying to close my UDT server (Netty 4.0.5.Final) with shutDownGracefully() and reopen it on the same port. Unfortunately, I always get the socket exception below although it waits until the future has completed. I also added the socket option SO_REUSEADDR. What is the proper way to do this? Exception in thread "main" com.barchart.udt.ExceptionUDT: UDT Error : 5011 : another socket is already listening on the same UDP port : listen0:listen [id: 0x323d3939] at com.barchart.udt.SocketUDT.listen0(Native Method) at com.barchart.udt.SocketUDT.listen(SocketUDT.java:1136) at com.barchart.udt.net.NetServerSocketUDT.bind(NetServerSocketUDT.java:66) at io.netty.channel.udt.nio.NioUdtAcceptorChannel.doBind(NioUdtAcceptorChannel.java:71) at io.netty.channel.AbstractChannel$AbstractUnsafe.bind(AbstractChannel.java:471) at io.netty.channel.DefaultChannelPipeline$HeadHandler.bind(DefaultChannelPipeline.java:1006) at io.netty.channel.DefaultChannelHandlerContext.invokeBind(DefaultChannelHandlerContext.java:504) at io.netty.channel.DefaultChannelHandlerContext.bind(DefaultChannelHandlerContext.java:487) at io.netty.channel.ChannelDuplexHandler.bind(ChannelDuplexHandler.java:38) at io.netty.handler.logging.LoggingHandler.bind(LoggingHandler.java:254) at io.netty.channel.DefaultChannelHandlerContext.invokeBind(DefaultChannelHandlerContext.java:504) at io.netty.channel.DefaultChannelHandlerContext.bind(DefaultChannelHandlerContext.java:487) at io.netty.channel.DefaultChannelPipeline.bind(DefaultChannelPipeline.java:848) at io.netty.channel.AbstractChannel.bind(AbstractChannel.java:193) at io.netty.bootstrap.AbstractBootstrap$2.run(AbstractBootstrap.java:321) at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:354) at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:366) at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) at java.lang.Thread.run(Thread.java:724) A small test program demonstration the problem: public class MsgEchoServer { public static class MsgEchoServerHandler extends ChannelInboundHandlerAdapter { } public void run() throws Exception { final ThreadFactory acceptFactory = new UtilThreadFactory("accept"); final ThreadFactory connectFactory = new UtilThreadFactory("connect"); final NioEventLoopGroup acceptGroup = new NioEventLoopGroup(1, acceptFactory, NioUdtProvider.MESSAGE_PROVIDER); final NioEventLoopGroup connectGroup = new NioEventLoopGroup(1, connectFactory, NioUdtProvider.MESSAGE_PROVIDER); try { final ServerBootstrap boot = new ServerBootstrap(); boot.group(acceptGroup, connectGroup) .channelFactory(NioUdtProvider.MESSAGE_ACCEPTOR) .option(ChannelOption.SO_BACKLOG, 10) .option(ChannelOption.SO_REUSEADDR, true) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer<UdtChannel>() { @Override public void initChannel(final UdtChannel ch) throws Exception { ch.pipeline().addLast(new MsgEchoServerHandler()); } }); final ChannelFuture future = boot.bind(1234).sync(); } finally { acceptGroup.shutdownGracefully().syncUninterruptibly(); connectGroup.shutdownGracefully().syncUninterruptibly(); } new MsgEchoServer().run(); } public static void main(final String[] args) throws Exception { new MsgEchoServer().run(); } }

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• Lightweight alternative to Manual/AutoResetEvent in C#

  - by sweetlilmre

  Hi, I have written what I hope is a lightweight alternative to using the ManualResetEvent and AutoResetEvent classes in C#/.NET. The reasoning behind this was to have Event like functionality without the weight of using a kernel locking object. Although the code seems to work well in both testing and production, getting this kind of thing right for all possibilities can be a fraught undertaking and I would humbly request any constructive comments and or criticism from the StackOverflow crowd on this. Hopefully (after review) this will be useful to others. Usage should be similar to the Manual/AutoResetEvent classes with Notify() used for Set(). Here goes: using System; using System.Threading; public class Signal { private readonly object _lock = new object(); private readonly bool _autoResetSignal; private bool _notified; public Signal() : this(false, false) { } public Signal(bool initialState, bool autoReset) { _autoResetSignal = autoReset; _notified = initialState; } public virtual void Notify() { lock (_lock) { // first time? if (!_notified) { // set the flag _notified = true; // unblock a thread which is waiting on this signal Monitor.Pulse(_lock); } } } public void Wait() { Wait(Timeout.Infinite); } public virtual bool Wait(int milliseconds) { lock (_lock) { bool ret = true; // this check needs to be inside the lock otherwise you can get nailed // with a race condition where the notify thread sets the flag AFTER // the waiting thread has checked it and acquires the lock and does the // pulse before the Monitor.Wait below - when this happens the caller // will wait forever as he "just missed" the only pulse which is ever // going to happen if (!_notified) { ret = Monitor.Wait(_lock, milliseconds); } if (_autoResetSignal) { _notified = false; } return (ret); } } }

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